U.S. Pat. No. 4,867,040 discloses a prior art semiautomatic rifle having a self unlocking device, (SUD) and is hereby incorporated by reference. The disclosed rifle design has been extremely successful for every intended application. However, for certain limited applications for which it was not intended, it is subject to malfunction, premature wear or breakage.
The prior art rifle may experience operating failures when certain types of muzzle-mounted sound suppressors are employed. Essentially, a sound suppressor temporarily retains much of the expanding propellant gases that would normally be immediately dispersed at the muzzle. The auto loading firearm unlocks its bolt as soon as the bore pressure drops to a safe level, but when shooting with a suppressor, some of the gas pressure is returned back through the bore of the barrel. This retrograde pressure wave acts on the empty cartridge casing, pushing it rearward like a piston. Thus, instead of the rearward motion of the bolt extracting the casing with tension and thereby absorbing some of the bolt's recoil energy, the recoil energy of the bolt is increased, which can cause enhanced wear or damage to various components such as buffers, magazine lips, and a carrier-to-bolt latch.
The retrograde pressure wave may prevent the bolt from properly extending, as would happen during extraction. Bolt extension is normally assured by a spring that biases the bolt away from the bolt carrier. However, the excessive pressure on the bolt face overwhelms the biasing force of the bolt spring. This can prevent a latch on the bolt carrier from engaging the bolt and locking it in an extended position while the bolt is recoiling and feeding a subsequent cartridge from the magazine. In addition, when the latch does engage, the force of the rearwardly-driven casing is transmitted from the bolt via the latch to the bolt carrier. The latch is not intended for transmitting such substantial forces, and is vulnerable to excessive wear and damage that may render it nonfunctional for its normal latching purpose.
In addition to the limited ability to withstand high bolt face pressures caused by the sound suppressors, the prior art rifle requires a bolt latch, a spring to bias the bolt latch, and a bolt spring, increasing the complexity of the bolt assembly, with the inherent disadvantages of complexity in any mechanical system.
The present invention overcomes the limitations of the prior art by providing a semiautomatic rifle having a housing containing a bolt carrier assembly that reciprocates along the housing axis. The bolt carrier assembly has a bolt, and reciprocates axially with respect to the carrier. A barrel is connected to the housing, and has a rear portion having a locking chamber that removably receives part of the bolt. An arm element interconnects the bolt carrier and the bolt, and operates to extend the bolt in response to rearward movement of the bolt carrier within the housing. The arm may be pivotally connected to the bolt carrier. The bolt carrier may include a rod internal of the bolt carrier, having a rear end contacting the arm, a mid section contacting the rear of the bolt via the bolt extender, and a forward end contacting the rear of the barrel.